Re: 'mail it in'

: : I looked forward with anticipation to a performance by
: : the group, 'Chicago, a while back when I was in Reno, Nevada. What a disapointment to hear an underwhelming and totally devoid of energy rendition of the old classics. One of the other members of the audience, who also left early, said -- 'they really mailed it in!'

: Similar to "phoned it in." I wonder which came first.

"Phoned it in" is likely to be first - because a newspaper reporter will phone-in their report to the news desk, whereas Chicago had no urgency about their performance and 'mailed' the show as a contrast to the urgency of the telephone.
if a reporter mailed a story, then that would suggest it was a feature that could wait, rather then a news story to be broken.